Charged particles include positively charged particles (e.g., protons and positive ions), and negatively charged particles (e.g., electrons and ions). In various devices, systems and applications, a beam of charged particles can be controlled to propagate (i.e. transported) towards a destination or target with a desired energy and beam profile. The beam profile can be controlled by using one or more charged particle lenses to focus, defocus or collimate the charged particle beam in a way similar to focusing, defocusing or collimating a beam of light using one or more optical lenses.
Charged particle lenses can be implemented in various ways, including magnetic lenses that use magnetic fields to control the charged particle beam profile or electrostatic lenses that use electrodes to produce a desired electric field profile for controlling the charged particle beam profile. One example of devices and systems based on charged particle beams is particle accelerators that increase the energy of electrically-charged particles, e.g., electrons, protons, or charged atomic nuclei. High energy electrically-charged atomic particles are accelerated to collide with target atoms, and the resulting products are observed with a detector. At very high energies the charged particles can break up the nuclei of the target atoms or molecules and interact with other particles. Transformations are produced that help to discern the nature and behavior of fundamental units of matter. Particle accelerators are also important tools in the effort to develop nuclear fusion devices, as well as in medical applications such as proton therapy for cancer treatment.
Proton therapy uses a beam of protons to irradiate diseased tissue, most often in the treatment of cancer. The proton beams can be utilized to more accurately localize the radiation dosage and provide better targeted penetration inside the human body when compared with other types of external beam radiotherapy. Due to their relatively large mass, protons have relatively small lateral side scatter in the tissue, which allows the proton beam to stay focused on the tumor with only low-dose side-effects to the surrounding tissue.
The radiation dose delivered by the proton beam to the tissue is at or near maximum just over the last few millimeters of the particle's range, known as the Bragg peak. Tumors closer to the surface of the body are treated using protons with lower energy. To treat tumors at greater depths, the proton accelerator must produce a beam with higher energy. By adjusting the energy of the protons during radiation treatment, the cell damage due to the proton beam is maximized within the tumor itself, while tissues that are closer to the body surface than the tumor, and tissues that are located deeper within the body than the tumor, receive reduced or negligible radiation.
Proton beam therapy systems are traditionally constructed using large accelerators that are expensive to build and hard to maintain. However, recent developments in accelerator technology are paving the way for reducing the footprint of the proton beam therapy systems that can be housed in a single treatment room. Such systems often require newly designed, or re-designed, subsystems that can successfully operate within the small footprint of the proton therapy system, reduce or eliminate health risks for patients and operators of the system, and provide enhanced functionalities and features.
In order to increase the effectiveness of radiation therapy, it is advantageous to be able to rapidly and dynamically vary the spot size of the charged particle beam at the targeted area, and to enable focusing and defocusing of the charged particle. Such capabilities, however, can be difficult to implement in various compact accelerator configurations.